Thursday, July 16, 2015

HEALTH and FITNESS traits: relative heritability and other observations

This is from the November 2012 Diary Newsletter

It continues to vary, from stud to stud, in how much emphasis is suggested you place on “health” traits relative to the production and type measures we have traditionally used in sire selection and index rank.
A cynic would say the stud that lacks in this area of gene inheritance will tell you “the heritability is too low to waste your time” [which is spurious advice— the heritabilities are often as great as the popular linear type traits they encourage you to consider].     By contrast, the stud that has focused on this area (as is true for any stud that preaches “Net Merit” indexing) will tell you it is so important you might as well forget about “type” altogether.

The truth is somewhere in the middle:   put each “trait group” in perspective

If you were to translate genetic statistics into their causative biology (something the industry really is not good at doing lately) you would figure out the following:

The bulk of the genotype as relates to production, reproduction, and health maintenance works in the fashion of competitively rationing nutrient energy between each of these needed functions.    As soon as a cow either falls into a negative energy state (insufficient appetite), faces a short feed supply (the main summer grazing problem), or faces a low energy ration (low forage quality), thus not meeting her energy requirements to perform all three functions, her genetic [trait] makeup will determine which (two or one) functions she will maintain, and which (one or two) systems will appear to fail.”

No amount of “health trait selection” will induce health where energy supply is inadequate

Graziers were the first to complain about the inadequacies of “modern” (purebred Holstein) genetics as they transitioned from barn or bunk feeding to turning the cows loose to fend for themselves.    No one who has switched from “conventional” to “grass” dairying can honestly say he did not either lose milk volume or cow health and fertility during the early years of their transition.

The truth of the matter was then (and still is now) that when your farm transitions from row crops and starch based rations to pasturage rotation and forage based rations, no one is producing the full yield of grass and related forages immediately.    Thus, the cows behaved as their genotypes dictated—those with enough “health” genes backed off on milk volume to stay healthy, while those who had mostly “milk” genes backed off on health to keep milking—and often, given the reproductive necessity for a rising energy plane, also delayed or ignored conception.

If your forage production is good enough to meet your cows’ needs, genetic ability can express itself.

Select for a  “balance” between (1) Production, (2) Reproduction, and (3) Health maintenance.

After multiple generations of emphasizing “milk” in sire selection, you will have “inbred” your cows for milk genes, over fertility and health genes.     A generation or two of “health trait” sires can restore that balance in the energy utilization gene package.     To continue to emphasize “health” over “milk” (as the earliest adapters of $Net Merit are learning) can, however, put a lid on young cow production.   It is as possible to “inbreed” health and fertility as it is to “inbreed” lack of health and infertility.    Thus your primary selection rule needs to be—over multiple generations, break the old rules, and vary selection to gain back any traits or qualities lost from the prior genetic focus.

Manage your farmland to produce an abundance of digestible fiber energy and protein in order to meet the full genetic ability and physiological requirements of your cows.

Many of us had to learn it the hard way—genetics that emphasized milk volume over milk component density were less healthy, and when combined with type emphasis on angularity, were less reproductive, than genetics that appeared to strike a balance between gaining milk while maintaining components and avoiding extreme physical type expressions.     Failure to provide good feed would bring these to light.

If you measured milk production by its caloric value (Energy Corrected yield) it became clear that your 80 pound Holstein cow (at 3.5%bf and 3.0%pr) was the same as a 55 pound Jersey cow (5.0%bf 3.7%pr)
Unfortunately, we live in a state where even DHIA (who should know better) still persists in “ranking” its patrons by monthly pounds of milk— thus confusing the genetic selection signals away from balance in mating selection.     (Many “color breed” herds refuse to test for this very reason, yet stay profitably in the dairy business—possibly proving that milk volume is not that important in creating profit margin.)

A key reason was the failure of geneticists to learn anything from nutritionists or veterinarians.    More milk just seemed like the better selection route, given the 1970s gave us class I bottling premiums and corn was a relatively cheap way to boost ration energy.   The heifer that will give the “most” milk is the heifer who possesses these (genetic) characteristics:

(1)  Faster physical maturity.    She is not only taller, she looks older—and may thus age faster.
(2)   Responds to improved ration energy density with volume rather than components.
(3)   Has indifferent (average or worse) somatic cell scores.     Her later lactations suffer for this.
(4)   Delays cycling after calving, delays conception until well past peak production, delays gains in  
      body conditioning until pregnant, loses persistency after pregnancy.    The unregulated metabolism
      this suggests leads to metabolic disease in later lactations, as well as more stillbirths.
(5)  Highly angular visual physique.     Get her to eat more, she just milks more, no matter what you do
       she will not gain body condition without highly expensive oilseed-based supplemental feed.

The statistics on which measures such as SCS (Somatic Cell Score), DPR (Daughter Pregnancy Rate), SB (stillbirths—direct and maternal) and ultimately PL (Productive Life) are calculated, all tended to show that the “fastest maturity” animals were ultimately the “fastest aging” and thus “least healthy” animals.    These factors in genetic combination resulted in the shortest functional herd longevity.

I was taught that “good type” insured longevity.     Was this wrong?

No—and Yes.    No, because poor type as evidenced by failing udders, poor legs and lame feet add up to a heifer that will not have a long life.    Yes, because “good type” cannot compensate for poor fertility, and in the opinion of research biologists, in every specie, fertility and will to live are strongly linked.
Given the trend in selection over so many decades was to favor young (newest pedigree) cows over “old” (proven longevity) cows as “bull mothers”, genes for longevity were mostly suppressed in favor of genes for faster maturity.    In parallel, the preferred herd for “bull mothers” and the preferred sampling environment for their AI sons was the higher herd average, thus higher external input “management” herds—herds considered as “challenging the genetics to see who will milk the most”.     This resulted in evaluation within environments that could hide genetic deficiencies in fertility and health under a higher level of management, nutrition and veterinary intervention.    Genomics is an evolution of this thinking, not a radical change in genetics.    Thus you still need to consider all other factors to breed better cows. 

The best view of “type” today is to understand a primary aspect of biological survival:  the physique must be adaptable to both the limitations and the variations of the realized enviroment.   Geneticists’ theorizing over a “model” environment for accurate evaluation is a complete failure to grasp biological implications of selection on “composite trait ranking” over actual longevity of competitive survival.
The cows with the greatest longevity of competitive production (your “old” cows) teach us what “best type” really is— even though they are currently being ignored for the Genomic base of comparison.

Pounds per Day of Life – the ultimate measure of a cow’s phenotype to reflect genotype profitability
“aAa” breeding guide – the ultimate method to insure a balanced, adaptable physique from matings
Our AI services are designed to help you find “profitable” genetics specific to the inheritance of your cows, and to enable matings that can produce cows with a full competitive lifetime.   Given all the ways in which cost of dairy production has climbed, controlling all manageable genetic effects has a place in producing replacement heifers that will produce milk profitably under “low maintenance” and reproduce optimally without constant veterinary intervention.     Longevity of production ultimately gives you the lowest replacement cost of production.     Longevity is highly heritable under mating selection.

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